Analysis of Clinical HIV-1 Strains with Resistance to Maraviroc Reveals Strain-Specific Resistance Mutations, Variable Degrees of Resistance, and Minimal Cross-Resistance to Other CCR5 Antagonists

Maraviroc (MVC) is an allosteric inhibitor of human immunodeficiency virus type 1 (HIV-1) entry, and is the only CCR5 antagonist licensed for use as an anti-HIV-1 therapeutic. It acts by altering the conformation of the CCR5 extracellular loops, rendering CCR5 unrecognizable by the HIV-1 envelope (Env) glycoproteins. This study aimed to understand the mechanisms underlying the development of MVC resistance in HIV-1-infected patients. To do this, we obtained longitudinal plasma samples from eight subjects who experienced treatment failure with phenotypically verified, CCR5-tropic MVC resistance. We then cloned and characterized HIV-1 Envs (n = 77) from plasma of pretreatment (n = 36) and treatment failure (n = 41) samples. Our results showed variation in the magnitude of MVC resistance as measured by reductions in maximal percent inhibition of Env-pseudotyped viruses, which was more pronounced in 293-Affinofile cells compared to other cells with similar levels of CCR5 expression. Amino acid determinants of MVC resistance localized to the V3 Env region and were strain specific. We also observed minimal cross-resistance to other CCR5 antagonists by MVC-resistant strains. We conclude that 293-Affinofile cells are highly sensitive for detecting and measuring MVC resistance through a mechanism that is CCR5-dependent yet independent of CCR5 expression levels. The strain-specific nature of resistance mutations suggests that sequence-based diagnostics and prognostics will need to be more sophisticated than simple position scoring to be useful for managing resistance in subjects taking MVC. Finally, the minimal levels of cross-resistance suggests that recognition of the MVC-modified form of CCR5 does not necessarily lead to recognition of other antagonist-modified forms of CCR5.

CNS-specific regulatory elements in brain-derived HIV-1 strains affect responses to latency-reversing agents with implications for cure strategies

Latency-reversing agents (LRAs), including histone deacetylase inhibitors (HDACi), are being investigated as a strategy to eliminate latency in HIV-infected patients on suppressive antiretroviral therapy. The effectiveness of LRAs in activating latent infection in HIV strains derived from the central nervous system (CNS) is unknown. Here we show that CNS-derived HIV-1 strains possess polymorphisms within and surrounding the Sp transcription factor motifs in the long terminal repeat (LTR). These polymorphisms result in decreased ability of the transcription factor specificity protein 1 to bind CNS-derived LTRs, reducing the transcriptional activity of CNS-derived viruses. These mutations result in CNS-derived viruses being less responsive to activation by the HDACi panobinostat and romidepsin compared with lymphoid-derived viruses from the same subjects. Our findings suggest that HIV-1 strains residing in the CNS have unique transcriptional regulatory mechanisms, which impact the regulation of latency, the consideration of which is essential for the development of HIV-1 eradication strategies.

Reliable genotypic tropism tests for the major HIV-1 subtypes

Over the past decade antiretroviral drugs have dramatically improved the prognosis for HIV-1 infected individuals, yet achieving better access to vulnerable populations remains a challenge. The principal obstacle to the CCR5-antagonist, maraviroc, from being more widely used in anti-HIV-1 therapy regimens is that the pre-treatment genotypic "tropism tests" to determine virus susceptibility to maraviroc have been developed primarily for HIV-1 subtype B strains, which account for only 10% of infections worldwide. We therefore developed PhenoSeq, a suite of HIV-1 genotypic tropism assays that are highly sensitive and specific for establishing the tropism of HIV-1 subtypes A, B, C, D and circulating recombinant forms of subtypes AE and AG, which together account for 95% of HIV-1 infections worldwide. The PhenoSeq platform will inform the appropriate use of maraviroc and future CCR5 blocking drugs in regions of the world where non-B HIV-1 predominates, which are burdened the most by the HIV-1 pandemic.

Ex vivo response to histone deacetylase (HDAC) inhibitors of the HIV long terminal repeat (LTR) derived from HIV-infected patients on antiretroviral therapy

Histone deacetylase inhibitors (HDACi) can induce human immunodeficiency virus (HIV) transcription from the HIV long terminal repeat (LTR). However, ex vivo and in vivo responses to HDACi are variable and the activity of HDACi in cells other than T-cells have not been well characterised. Here, we developed a novel assay to determine the activity of HDACi on patient-derived HIV LTRs in different cell types. HIV LTRs from integrated virus were amplified using triple-nested Alu-PCR from total memory CD4+ T-cells (CD45RO+) isolated from HIV-infected patients prior to and following suppressive antiretroviral therapy. NL4-3 or patient-derived HIV LTRs were cloned into the chromatin forming episomal vector pCEP4, and the effect of HDACi investigated in the astrocyte and epithelial cell lines SVG and HeLa, respectively. There were no significant differences in the sequence of the HIV LTRs isolated from CD4+ T-cells prior to and after 18 months of combination antiretroviral therapy (cART). We found that in both cell lines, the HDACi panobinostat, trichostatin A, vorinostat and entinostat activated patient-derived HIV LTRs to similar levels seen with NL4-3 and all patient derived isolates had similar sensitivity to maximum HDACi stimulation. We observed a marked difference in the maximum fold induction of luciferase by HDACi in HeLa and SVG, suggesting that the effect of HDACi may be influenced by the cellular environment. Finally, we observed significant synergy in activation of the LTR with vorinostat and the viral protein Tat. Together, our results suggest that the LTR sequence of integrated virus is not a major determinant of a functional response to an HDACi.

HIV-1 transcriptional regulation in the central nervous system and implications for HIV cure research

Human immunodeficiency virus type-1 (HIV-1) invades the central nervous system (CNS) during acute infection which can result in HIV-associated neurocognitive disorders in up to 50% of patients, even in the presence of combination antiretroviral therapy (cART). Within the CNS, productive HIV-1 infection occurs in the perivascular macrophages and microglia. Astrocytes also become infected, although their infection is restricted and does not give rise to new viral particles. The major barrier to the elimination of HIV-1 is the establishment of viral reservoirs in different anatomical sites throughout the body and viral persistence during long-term treatment with cART. While the predominant viral reservoir is believed to be resting CD4(+) T cells in the blood, other anatomical compartments including the CNS, gut-associated lymphoid tissue, bone marrow, and genital tract can also harbour persistently infected cellular reservoirs of HIV-1. Viral latency is predominantly responsible for HIV-1 persistence and is most likely governed at the transcriptional level. Current clinical trials are testing transcriptional activators, in the background of cART, in an attempt to purge these viral reservoirs and reverse viral latency. These strategies aim to activate viral transcription in cells constituting the viral reservoir, so they can be recognised and cleared by the immune system, while new rounds of infection are blocked by co-administration of cART. The CNS has several unique characteristics that may result in differences in viral transcription and in the way latency is established. These include CNS-specific cell types, different transcription factors, altered immune surveillance, and reduced antiretroviral drug bioavailability. A comprehensive understanding of viral transcription and latency in the CNS is required in order to determine treatment outcomes when using transcriptional activators within the CNS.

HIV-1 entry and trans-infection of astrocytes involves CD81 vesicles

Astrocytes are extensively infected with HIV-1 in vivo and play a significant role in the development of HIV-1-associated neurocognitive disorders. Despite their extensive infection, little is known about how astrocytes become infected, since they lack cell surface CD4 expression. In the present study, we investigated the fate of HIV-1 upon infection of astrocytes. Astrocytes were found to bind and harbor virus followed by biphasic decay, with HIV-1 detectable out to 72 hours. HIV-1 was observed to associate with CD81-lined vesicle structures. shRNA silencing of CD81 resulted in less cell-associated virus but no loss of co-localization between HIV-1 and CD81. Astrocytes supported trans-infection of HIV-1 to T-cells without de novo virus production, and the virus-containing compartment required 37°C to form, and was trypsin-resistant. The CD81 compartment observed herein, has been shown in other cell types to be a relatively protective compartment. Within astrocytes, this compartment may be actively involved in virus entry and/or spread. The ability of astrocytes to transfer virus, without de novo viral synthesis suggests they are capable of sequestering and protecting virus and thus, they could potentially facilitate viral dissemination in the CNS.

A common mechanism of clinical HIV-1 resistance to the CCR5 antagonist maraviroc despite divergent resistance levels and lack of common gp120 resistance mutations

Background

The CCR5 antagonist maraviroc (MVC) inhibits human immunodeficiency virus type 1 (HIV-1) entry by altering the CCR5 extracellular loops (ECL), such that the gp120 envelope glycoproteins (Env) no longer recognize CCR5. The mechanisms of HIV-1 resistance to MVC, the only CCR5 antagonist licensed for clinical use are poorly understood, with insights into MVC resistance almost exclusively limited to knowledge obtained from in vitro studies or from studies of resistance to other CCR5 antagonists. To more precisely understand mechanisms of resistance to MVC in vivo, we characterized Envs isolated from 2 subjects who experienced virologic failure on MVC.

Results

Envs were cloned from subjects 17 and 24 before commencement of MVC (17-Sens and 24-Sens) and after virologic failure (17-Res and 24-Res). The Envs cloned during virologic failure showed broad divergence in resistance levels, with 17-Res Env exhibiting a relatively high maximal percent inhibition (MPI) of ~90% in NP2-CD4/CCR5 cells and peripheral blood mononuclear cells (PBMC), and 24-Res Env exhibiting a very low MPI of ~0 to 12% in both cell types, indicating relatively “weak” and “strong” resistance, respectively. Resistance mutations were strain-specific and mapped to the gp120 V3 loop. Affinity profiling by the 293-Affinofile assay and mathematical modeling using VERSA (Viral Entry Receptor Sensitivity Analysis) metrics revealed that 17-Res and 24-Res Envs engaged MVC-bound CCR5 inefficiently or very efficiently, respectively. Despite highly divergent phenotypes, and a lack of common gp120 resistance mutations, both resistant Envs exhibited an almost superimposable pattern of dramatically increased reliance on sulfated tyrosine residues in the CCR5 N-terminus, and on histidine residues in the CCR5 ECLs. This altered mechanism of CCR5 engagement rendered both the resistant Envs susceptible to neutralization by a sulfated peptide fragment of the CCR5 N-terminus.

Conclusions

Clinical resistance to MVC may involve divergent Env phenotypes and different genetic alterations in gp120, but the molecular mechanism of resistance of the Envs studied here appears to be related. The increased reliance on sulfated CCR5 N-terminus residues suggests a new avenue to block HIV-1 entry by CCR5 N-terminus sulfopeptidomimetic drugs.

The NRTIs lamivudine, stavudine and zidovudine have reduced HIV-1 inhibitory activity in astrocytes

HIV-1 establishes infection in astrocytes and macroage-lineage cells of the central nervous system (CNS). Certain antiretroviral drugs (ARVs) can penetrate the CNS, and are therefore often used in neurologically active combined antiretroviral therapy (Neuro-cART) regimens, but their relative activity in the different susceptible CNS cell populations is unknown. Here, we determined the HIV-1 inhibitory activity of CNS-penetrating ARVs in astrocytes and macrophage-lineage cells. Primary human fetal astrocytes (PFA) and the SVG human astrocyte cell line were used as in vitro models for astrocyte infection, and monocyte-derived macrophages (MDM) were used as an in vitro model for infection of macrophage-lineage cells. The CNS-penetrating ARVs tested were the nucleoside reverse transcriptase inhibitors (NRTIs) abacavir (ABC), lamivudine (3TC), stavudine (d4T) and zidovudine (ZDV), the non-NRTIs efavirenz (EFV), etravirine (ETR) and nevirapine (NVP), and the integrase inhibitor raltegravir (RAL). Drug inhibition assays were performed using single-round HIV-1 entry assays with luciferase viruses pseudotyped with HIV-1 YU-2 envelope or vesicular stomatitis virus G protein (VSV-G). All the ARVs tested could effectively inhibit HIV-1 infection in macrophages, with EC90s below concentrations known to be achievable in the cerebral spinal fluid (CSF). Most of the ARVs had similar potency in astrocytes, however the NRTIs 3TC, d4T and ZDV had insufficient HIV-1 inhibitory activity in astrocytes, with EC90s 12-, 187- and 110-fold greater than achievable CSF concentrations, respectively. Our data suggest that 3TC, d4T and ZDV may not adequately target astrocyte infection in vivo, which has potential implications for their inclusion in Neuro-cART regimens.

CoRSeqV3-C: a novel HIV-1 subtype C specific V3 sequence based coreceptor usage prediction algorithm

Background

The majority of HIV-1 subjects worldwide are infected with HIV-1 subtype C (C-HIV). Although C-HIV predominates in developing regions of the world such as Southern Africa and Central Asia, C-HIV is also spreading rapidly in countries with more developed economies and health care systems, whose populations are more likely to have access to wider treatment options, including the CCR5 antagonist maraviroc (MVC). The ability to reliably determine C-HIV coreceptor usage is therefore becoming increasingly more important. In silico V3 sequence based coreceptor usage prediction algorithms are a relatively rapid and cost effective method for determining HIV-1 coreceptor specificity. In this study, we elucidated the V3 sequence determinants of C-HIV coreceptor usage, and used this knowledge to develop and validate a novel, user friendly, and highly sensitive C-HIV specific coreceptor usage prediction algorithm.

Results

We characterized every phenotypically-verified C-HIV gp120 V3 sequence available in the Los Alamos HIV Database. Sequence analyses revealed that compared to R5 C-HIV V3 sequences, CXCR4-using C-HIV V3 sequences have significantly greater amino acid variability, increased net charge, increased amino acid length, increased frequency of insertions and substitutions within the GPGQ crown motif, and reduced frequency of glycosylation sites. Based on these findings, we developed a novel C-HIV specific coreceptor usage prediction algorithm (CoRSeq_V3-C), which we show has superior sensitivity for determining CXCR4 usage by C-HIV strains compared to all other available algorithms and prediction rules, including Geno2pheno_[coreceptor] and WebPSSM_SINSI-C, which has been designed specifically for C-HIV.

Conclusions

CoRSeq_V3-C is now openly available for public use at http://www.burnet.edu.au/coreceptor. Our results show that CoRSeq_V3-C is the most sensitive V3 sequence based algorithm presently available for predicting CXCR4 usage of C-HIV strains, without compromising specificity. CoRSeq_V3-C may be potentially useful for assisting clinicians to decide the best treatment options for patients with C-HIV infection, and will be helpful for basic studies of C-HIV pathogenesis.

Reduced basal transcriptional activity of central nervous system-derived HIV type 1 long terminal repeats

New evidence indicates that astrocytes of the central nervous system (CNS) are extensively infected with human immunodeficiency virus type 1 (HIV-1) in vivo. Although no new virus is produced, this nonproductive or restricted infection contributes to the pathogenesis of HIV-associated dementia (HAD) and compromises virus eradication strategies. The HIV-1 long terminal repeat (LTR) plays a critical role in regulating virus production from infected cells. Here, we determined whether LTRs derived from CNS and non-CNS compartments are genetically and functionally distinct and contribute to the restricted nature of astrocyte infection. CNS- and/or non-CNS-derived LTRs (n=82) were cloned from primary HIV-1 viruses isolated from autopsy tissues of seven patients who died with HAD. Phylogenetic analysis showed interpatient and intrapatient clustering of LTR nucleotide sequences. Functional analysis showed reduced basal transcriptional activity of CNS-derived LTRs in both astrocytes and T cells compared to that of non-CNS-derived LTRs. However, LTRs were heterogeneous in their responsiveness to activation by Tat. Therefore, using a relatively large, independent panel of primary HIV-1 LTRs derived from clinically well-characterized subjects, we show that LTRs segregate CNS- from non-CNS-derived tissues both genetically and functionally. The reduced basal transcriptional activity of LTRs derived from the CNS may contribute to the restricted HIV-1 infection of astrocytes and latent infection within the CNS. These findings have significance for understanding the molecular basis of HIV-1 persistence within cellular reservoirs of the CNS that need to be considered for strategies aimed at eradicating HIV-1.

Macrophage-tropic HIV-1 variants from brain demonstrate alterations in the way gp120 engages both CD4 and CCR5

BR-derived HIV-1 strains have an exceptional ability to enter macrophages via mechanisms involving their gp120 Env that remain incompletely understood. Here, we used cell-based affinity-profiling methods and mathematical modeling to generate quantitative VERSA metrics that simultaneously measure Env-CD4 and Env-CCR5 interactions. These metrics were analyzed to distinguish the phenotypes of M-tropic and non-M-tropic CCR5-using HIV-1 variants derived from autopsy BRs and LNs, respectively. We show that highly M-tropic Env variants derived from brain can be defined by two distinct and simultaneously occurring phenotypes. First, BR-derived Envs demonstrated an enhanced ability to interact with CD4 compared with LN-derived Envs, permitting entry into cells expressing scant levels of CD4. Second, BR-derived Envs displayed an altered mechanism of engagement between CD4-bound gp120 and CCR5 occurring in tandem. With the use of epitope mapping, mutagenesis, and structural studies, we show that this altered mechanism is characterized by increased exposure of CD4-induced epitopes in gp120 and by a more critical interaction between BR-derived Envs and the CCR5 N-terminus, which was associated with the predicted presence of additional atomic contacts formed at the gp120-CCR5 N-terminus interface. Our results suggest that BR-derived HIV-1 variants with highly efficient macrophage entry adopt conformations in gp120 that simultaneously alter the way in which the Env interacts with CD4 and CCR5.

A new way of measuring apoptosis by absolute quantitation of inter-nucleosomally fragmented genomic DNA

Several critical events of apoptosis occur in the cell nucleus, including inter-nucleosomal DNA fragmentation (apoptotic DNA) and eventual chromatin condensation. The generation of apoptotic DNA has become a biochemical hallmark of apoptosis because it is a late ‘point of no return’ step in both the extrinsic (cell-death receptor) and intrinsic (mitochondrial) apoptotic pathways. Despite investigators observing apoptotic DNA and understanding its decisive role as a marker of apoptosis for over 20 years, measuring it has proved elusive. We have integrated ligation-mediated PCR and qPCR to design a new way of measuring apoptosis, termed ApoqPCR, which generates an absolute value for the amount (picogram) of apoptotic DNA per cell population. ApoqPCR’s advances over current methods include a 1000-fold linear dynamic range yet sensitivity to distinguish subtle low-level changes, measurement with a 3- to 4-log improvement in sample economy, and capacity for archival or longitudinal studies combined with high-throughput capability. We demonstrate ApoqPCR’s utility in both in vitro and in vivo contexts. Considering the fundamental role apoptosis has in vertebrate and invertebrate health, growth and disease, the reliable measurement of apoptotic nucleic acid by ApoqPCR will be of value in cell biology studies in basic and applied science.

Genetic and functional heterogeneity of CNS-derived tat alleles from patients with HIV-associated dementia

Human immunodeficiency virus type 1 (HIV-1) demonstrates a high degree of viral diversity which has an impact on viral fitness. Genetic compartmentalization of HIV-1 proteins between central nervous system (CNS) and lymphoid tissues is well established and reflects altered requirements for HIV-1 replication in macrophages/microglia, brain-specific immune selection pressures and possibly the timing of virus invasion of the CNS. Tat-encoding mRNA has been detected in the CNS of HIV-1 infected individuals and its neurotoxic effects in the CNS are well documented. However, while CNS-derived tat sequences have demonstrated significant diversity, the effect of this molecular diversity on transcriptional regulation and its impact on the pathogenesis of HIV-associated dementia (HAD) remains unclear. In this study, we cloned and characterised 44 unique tat alleles from brain, cerebral spinal fluid, spinal cord and blood/lymphoid tissue-derived HIV-1 isolates from five subjects with HAD. While phylogenetic analyses revealed tissue-specific compartmentalization of Tat variants for two patients, broad compartmentalization across the panel of tissue-derived viruses was not observed. Despite the lack of consistent tissue-specific compartmentalization, sequence variations within patients segregated CNS and non-CNS tat alleles. These amino acid alterations predominated within the transactivation domain of Tat and could account for alterations in the ability of particular Tat proteins to transactivate the LTR. Although a subset of patients demonstrated reduced transactivation capacity among CNS-derived Tat proteins compared to those from matched lymphoid tissues, overall Tat proteins from the CNS to lymphoid compartments maintained similar levels of transactivation function. Together, these data suggest that despite the observed heterogeneity in tat alleles isolated from matched lymphoid to CNS compartments, Tat function is maintained, highlighting the importance of Tat function in HIV-1 neuropathogenesis.

CD4 and MHC class 1 down-modulation activities of nef alleles from brain- and lymphoid tissue-derived primary HIV-1 isolates

Human immunodeficiency virus type 1 (HIV-1) nef undergoes adaptive evolution in the central nervous system (CNS), reflecting altered requirements for HIV-1 replication in macrophages/microglia and brain-specific immune selection pressures. The role of Nef in HIV-1 neurotropism and pathogenesis of HIV-associated dementia (HAD) is unclear. In this study, we characterized 82 nef alleles cloned from brain, cerebral spinal fluid, spinal cord, and blood/lymphoid tissue-derived HIV-1 isolates from seven subjects with HAD. CNS isolate-derived nef alleles were genetically compartmentalized and had reduced sequence diversity compared to those from lymphoid tissue isolates. Defective nef alleles predominated in a brain-derived isolate from one of the seven subjects (MACS2-br). The ability of Nef to down-modulate CD4 and MHC class 1 (MHC-1) was generally conserved among nef alleles from both CNS and lymphoid tissues. However, the potency of CD4 and MHC-1 down-modulation was variable, which was associated with sequence alterations known to influence these Nef functions. These results suggest that CD4 and MHC-1 down-modulations are highly conserved functions among nef alleles from CNS- and lymphoid tissue-derived HIV-1 isolates that may contribute to viral replication and escape from immune surveillance in the CNS.

An altered and more efficient mechanism of CCR5 engagement contributes to macrophage tropism of CCR5-using HIV-1 envelopes

While CCR5 is the principal coreceptor used by macrophage (M)-tropic HIV-1, not all primary CCR5-using (R5) viruses enter macrophages efficiently. Here, we used functionally-diverse R5 envelope (Env) clones to characterize virus-cell interactions important for efficient CCR5-mediated macrophage entry. The magnitude of macrophage entry by Env-pseudotyped reporter viruses correlated with increased immunoreactivity of CD4-induced gp120 epitopes, increased ability to scavenge low levels of cell-surface CCR5, reduced sensitivity to the CCR5 inhibitor maraviroc, and increased dependence on specific residues in the CCR5 ECL2 region. These results are consistent with an altered and more efficient mechanism of CCR5 engagement. Structural studies revealed potential alterations within the gp120 V3 loop, the gp41 interaction sites at the gp120 C- and N-termini, and within the gp120 CD4 binding site which may directly or indirectly lead to more efficient CCR5-usage. Thus, enhanced gp120-CCR5 interactions may contribute to M-tropism of R5 HIV-1 strains through different structural mechanisms.

Asn 362 in gp120 contributes to enhanced fusogenicity by CCR5-restricted HIV-1 envelope glycoprotein variants from patients with AIDS

BACKGROUND

CCR5-restricted (R5) human immunodeficiency virus type 1 (HIV-1) variants cause CD4+ T-cell loss in the majority of individuals who progress to AIDS, but mechanisms underlying the pathogenicity of R5 strains are poorly understood. To better understand envelope glycoprotein (Env) determinants contributing to pathogenicity of R5 viruses, we characterized 37 full-length R5 Envs from cross-sectional and longitudinal R5 viruses isolated from blood of patients with asymptomatic infection or AIDS, referred to as pre-AIDS (PA) and AIDS (A) R5 Envs, respectively.

RESULTS

Compared to PA-R5 Envs, A-R5 Envs had enhanced fusogenicity in quantitative cell-cell fusion assays, and reduced sensitivity to inhibition by the fusion inhibitor T-20. Sequence analysis identified the presence of Asn 362 (N362), a potential N-linked glycosylation site immediately N-terminal to CD4-binding site (CD4bs) residues in the C3 region of gp120, more frequently in A-R5 Envs than PA-R5 Envs. N362 was associated with enhanced fusogenicity, faster entry kinetics, and increased sensitivity of Env-pseudotyped reporter viruses to neutralization by the CD4bs-directed Env mAb IgG1b12. Mutagenesis studies showed N362 contributes to enhanced fusogenicity of most A-R5 Envs. Molecular models indicate N362 is located adjacent to the CD4 binding loop of gp120, and suggest N362 may enhance fusogenicity by promoting greater exposure of the CD4bs and/or stabilizing the CD4-bound Env structure.

CONCLUSION

Enhanced fusogenicity is a phenotype of the A-R5 Envs studied, which was associated with the presence of N362, enhanced HIV-1 entry kinetics and increased CD4bs exposure in gp120. N362 contributes to fusogenicity of R5 Envs in a strain dependent manner. Our studies suggest enhanced fusogenicity of A-R5 Envs may contribute to CD4+ T-cell loss in subjects who progress to AIDS whilst harbouring R5 HIV-1 variants. N362 may contribute to this effect in some individuals.

Human immunodeficiency virus type 1 stimulates the expression and production of secretory leukocyte protease inhibitor (SLPI) in oral epithelial cells: a role for SLPI in innate mucosal immunity

The innate immune response is a key barrier against pathogenic microorganisms such as human immunodeficiency virus type 1 (HIV-1). Because HIV-1 is rarely transmitted orally, we hypothesized that oral epithelial cells participate in the innate immune defense against this virus. We further hypothesized that secretory leukocyte protease inhibitor (SLPI), a 12-kDa mucosal antiviral protein, is a component of the host immune response to this virus. Here we demonstrated constitutive expression and production of SLPI in immortalized human oral keratinocytes. Brief exposure of cells to HIV-1 BaL and HXB2 significantly increased SLPI mRNA and protein production compared to that in mock-exposed cells (P < 0.01), as evaluated by real-time quantitative reverse transcription-PCR and enzyme-linked immunosorbent assay. HIV-1-mediated stimulation of SLPI occurred at the transcriptional level, was dose and time dependent, was elicited by heat-inactivated and infectious viruses, and did not depend on cellular infection. Experiments with purified retroviral proteins showed that the stimulatory effect was induced specifically by external envelope glycoproteins from HIV-1 and simian immunodeficiency virus. SLPI responsiveness to HIV-1 was also observed in an unrelated oral epithelial cell line and in normal (nonimmortalized) human oral epithelial cells isolated from healthy uninfected gingival tissues. In this first report of SLPI regulation by HIV-1, we show that the expression and production of the antimicrobial and anti-inflammatory protein can be stimulated in oral epithelial cells by the virus through interactions with gp120 in the absence of direct infection. These findings indicate that SLPI is a component of the oral mucosal response to HIV-1.

Hyper-excretion of human immunodeficiency virus type 1 RNA in saliva

Anatomical compartments (e.g., the reproductive tract) are reservoirs of human immunodeficiency virus type-1 (HIV-1) and potential sites of residual infection in patients receiving anti-retroviral therapy (ART). Viral hyper-excretion relative to blood is a hallmark of reservoirs. To determine whether hyper-excretion can occur in the oral cavity, we compared viral loads in blood plasma and saliva of 67 adults. Salivary viral hyperexcretion was defined as a four-fold or higher viral load in saliva than in plasma. HIV-1 RNA was detected in 79% of plasma samples, in 44% of unfiltered saliva samples, in 16% of filtered saliva samples, and in 59% of saliva-derived cell pellets. Compared with non-hyper-excretors (n = 62), hyper-excretors (n = 5) had elevated levels of viral RNA in unfiltered saliva and saliva-derived cells, HIV-associated periodontal disease, gingival inflammation, and no combination ART. Morphological characterization of cell pellets identified lymphocytes as a likely HIV-1 source. These collective findings are consistent with an oral HIV-1 reservoir in selected individuals.